1. Field of the Invention
This invention relates to single ply reinforced roofing membranes for covering industrial and commercial flat roofs, and, more particularly, to such membranes having significantly improved tensile and seam strength properties.
2. Description of the Prior Art
Heat-sealable, reinforced polyolefin-based single ply roofing membranes are composed of base (bottom) and cap (top) polyolefin-based sheets (layers) with a fiber reinforcement scrim (middle) sandwiched between the other two layers. The scrim is the strongest layer in the composite. In order to fully realize the reinforcement properties of the scrim in such a laminate composite, however, it is necessary that excellent adhesion exist between the polyolefin sheets and the scrim. Unfortunately, due to the inherent incompatibility of scrim materials and polyolefins, only relatively poor interfacial adhesion exists between the scrim and polyolefin sheets. As a result, the roofing membrane is observed to have only low tensile and seam strength properties.
Accordingly, it is an object of this invention to modify the surface characteristics of one or both of the polyolefin-based layers in order to improve the interfacial bonding between polyolefin and scrim thus proving roofing membranes having enhanced membrane tensile and seam strengths.
This and other objects and features of the invention will be made apparent from the following description thereof.
In this invention, a small amount of a highly-flowable, functional-polyolefin is incorporated into one or both polyolefin-based roofing sheets of a single ply roofing membrane to modify the surface polarity of the polyolefin sheets therein. The resulting composite membrane of the invention exhibits substantially improved adhesion between the reinforcement scrim and the polyolefin sheets. As a result, the tensile and seam strengths of the membrane is advantageously increased.
In accordance with the invention, there is provided a single ply reinforced roofing membrane having significantly improved tensile and seam strengths. The membrane comprises a reinforcement scrim sandwiched between polyolefin cap and base layers, and is particularly characterized in that at least one of these layers includes a functional-polyolefin as additive therein. The thickness of the membrane preferably ranges from 5 to 200 mils, more preferably from 35-90 mils.
Suitably the single ply reinforced roofing membrane of the invention includes about 0.5-20% by wt. of the functional-polyolefin additive in one of said layers, preferably about 1-10%, and most preferably about 1-5%.
The functional polyolefin additive is suitably selected from polyolelfins which have been modified with one or more functional groups, such as carboxyl. epoxy, anhydride, amine, ester, (meth)acrylate and succinimide groups.
These functional groups can affect the surface of the polyolefin sheets so that it can adhere better to the scrim material. A maleic anhydride-modified polyolefin (CK Witco), an epoxy-modified polyethylene (Elf Atochem) and methyacrylate terpolymers thereof (Elf) are preferred.
Suitable polyolefins are polymers such as polyethylene, polypropylene, terpolymers of ethylene, propylene and diene monomers, ethylene-propylene copolymers, ethylene-butene copolymers, ethylene-hexene copolymers, ethylene-octene copolymers, propylene-C4-8 alpha-olefin copolymers, metallocene polyolefins and the like.
A preferred functional polyolefin for use herein is maleic anhydride-modified polypropylene sold by CK Witco.